Mendel’s Legacy

2. Mendel’s Legacy Genetics is everywhere these days – and it will continue to become even more important in decades to come. So wouldn’t it be nice if people understood it better?

3. Terms to Know and Use • Genetics – the study of heredity • Heredity – the passing of traits from the • parents to their offspring

4. Trait - variations of a gene: (i.e. black or brown hair) determined by alleles • Allele – different forms a gene, often expressed as Y or y, X or x, Z or z • Gene - a heritable feature on a chromosome: • (i.e. hair color)

5. Chromosome - strand of DNA that codes for genes • Locus - location of a gene, or allele, on a chromosome • Monohybrid cross – cross involving parents • differing in only 1 trait • True-breeding- organisms that always pass • the same genes to their offspring

6. Dominant trait- expressed over a recessive trait when both are present • Recessive trait- not expressed when the dominant trait is present • Homozygous – when both alleles of a gene are • the same (i.e. pure, TT) • Heterozygous – when the two alleles are not • the same (i.e. hybrid, Tt)

7. Genotype - the type of alleles on a chromosome: (gene makeup) Phenotype - The way a genotype is expressed: (physical appearance)

8. 1822- 1884 Austrian monk Experimented with pea plants Trained in math and science Gregor Johann Mendel“Father of Genetics”

9. Garden Pea Experiments 1856-64 Why pea plants? (Pisium sativum) Because they… • Were easy to grow • Produced a large number of offspring • Matured quickly • Had both male and female parts

10. The Problem T.A. Knight, a scientist, saw that if he crossed true bred true bred purple pea plant(P)x white pea plant (P) ALL the offspring would bepurple (F1).

11. The Problem (cont’d) If he then crossed the purple (F1) offspring: hybrid hybrid purple pea plant (F1) x white pea plant (F1) Most offspring arepurple (F2)&few white (F2).

12. Mendel’s Answer Mendel used math with science to explain heredity. He counted: 705 purple 224 white total 929 pea plants Thus he saw a 3:1 ratio.

13. Mendel’s Answer (cont’d) To explain this ratio he came up with Rules of Heredity • Parents transmit “genes” to offspring 2) Each individual has 2 genes (1 from each parent) 3) Some “genes” are dominant and others recessive

14. Mother contributes: P Generation P P or p Pp Pp or Father contributes: Pp Pp p

15. Mother contributes: F1 Generation P p or P Pp PP or Father contributes: pp Pp p

16. Lucky or Right On? Mendel repeated his experiments while observing other traits such as: • height of plant (tall vs. short) • pod appearance (inflated vs. constricted) • pod color (green vs. yellow) • seed texture (round vs. wrinkled) • seed color (yellow vs. green)

17. Pea Characteristics Trait on the left is dominant. Trait on the right is recessive.

19. Mendel's Laws of Inheritance • Law of Segregation- states that the two alleles separate when gametes (sperm/egg) form. Thus, a gamete receives only one allele from each parent. (test cross) • Law of Independent Assortment- states that different alleles (traits) separate independently. Thus, color, height, pod shape, etc. are not connected together. (dihybrid cross)

20. Determining Unknown Genotypes • How do you know if a dominant phenotype is homozygous or heterozygous? • Scientists can perform a test cross, where they cross the unknown with a recessive (known) phenotype.

21. Mother contributes: OPTION 1: Test Cross a a or A Aa Aa or Father contributes: Aa Aa A

22. Mother contributes: OPTION 2: Test Cross a a or A Aa Aa or Father contributes: aa aa a

23. Mendel's Laws of Inheritance • Law of Segregation- states that the two alleles separate when gametes (sperm/egg) form. Thus, a gamete receives only one allele from each parent. (test cross) • Law of Independent Assortment- states that different alleles (traits) separate independently. Thus, color, height, pod shape, etc. are not connected together. (dihybrid cross)

24. Mother contributes: Dihybrid Cross SB Sb sB sb SB SsBb SSBB SSBb SsBB Sb SSbB SsbB Ssbb SSbb Father contributes: sB sSBB sSBb ssBB ssBb sb sSbB sSbb ssbB ssbb

25. Dihybrid Cross

26. wrinkled wrinkled Smooth Smooth Smooth Tall Tall short Tall short Two chromosomes of one parent are represented on the left. Possible alleles passed on to the offspring are on the right. (Consider smooth or wrinkled peas AND tall or short plants)

27. DO ALL GENES ASSORT INDEPENDENTLY? • Genes on the same chromosome tend to be inherited together = linked • Sex-linked genes: color blindness, MD, hemophilia. X Y • X X

28. Chromosomes = DNA

29. Meiosis I One diploid sex cell divides……

30. Meiosis II Result: One diploid cell = four haploid cells

31. Crossing Over in Meiosis I

32. Credits • Mendel Image: pw1.netcom.com/~aguldo/ agga/bt/txt/bt1899.htm • Pea trellis: http://www.floridata.com/ref/p/images/pisu_sa1.jpg • Experiments in Plant Hybridization (1865)by Gregor Mendel Read at the meetings of February 8th, and March 8th, 1865 to the the Natural History Society of Brünn(paper can be read at: http://www.mendelweb.org/home.html • MendelWeb, edited by Roger B. Blumberg. (http://www.netspace.org/MendelWeb/, Edition 97.1 1997) • The Biology Project: http://www.biology.arizona.edu/default.html • Meiosis Images: www.micro.utexas.edu/.../bio304/ genetics/meiosis.4.gif • Crossing Over image: http://medlib.med.utah.edu/block2/biochem/Formosa/Figures/Lecture5/5-15%20Meiosis.JPG • Monohybrid, dihybrid, test cross & pea flower: ntri.tamuk.edu/homepage-ntri/lectures/ biology/test-cross.gi

33. Any Questions? • “The problem with the gene pool is that there is no lifeguard.” —Unknown • “Life can only be understood backwards; but it must be lived forwards.” —Kierkegaard